When you walk into the Great Hall in what order (from left to right) are the house tables in?
From what I can gather from the first book and Harry's description during the sorting ceremony, the tables appear to be like this from his point of view: Gryffindor on the far left, then Ravenclaw, then Slytherin, then Hufflepuff at the far right. However because this is from Harry's point of view as he stands at the front of the hall next to the teacher's table and facing the students. So I think that when you enter the hall, it might be reversed: with Hufflepuff on the far left, then Slytherin, Ravenclaw and Gryffindor.
Do you think they change each year, or does their order stay the same through out all of the seven books?
I want to say they stay the same, but after thinking about the scene in Deathly Hallows where the students in Gryffindor, Hufflepuff and Ravenclaw all stand up to protect Harry after Pansy Parkinson shouts to grab him implies that the Hufflepuff table is between Slytherin and Gryffindor. In fact, from that line and following descriptions, it sounds like the order goes: Slytherin, Ravenclaw, Hufflepuff, Gryffindor.
Maybe, like the staircases and all of the other oddities at Hogwarts, the tables get switched around just to throw the students off, but I don't think so. Harry is always described as going directly to the Gryffindor table without any problems, implying that it's always in the same place.
I think that the tables stay the same, but J.K. Rowling just messed up on the exact order and switched the Hufflepuff table and the Slytherin table around. Really, I think you can go with any order you want.